A typical hypodermic syringe includes a transparent cylindrical barrel, generally open at a proximal end, a plunger assembly movable within the barrel to dispense medication, and a needle assembly removably attached to the barrel at a distal end by means of a locking mechanism, such as Luer lock or Luer slip. During usage, medication is sealed within open side of the barrel by means of a rubber piston slipped over the distal end of the plunger. At the distal end of the syringe, sealing is accomplished through a sealant, such as an epoxy resin, extending between the outer surface of the needle and the lock hub carrying the needle. This sealant, and the locking mechanism fastening the needle assembly to the barrel, are also used to transmit the force, which may be as high as several pounds, required to insert the needle into the patient's body and to remove the needle after the injection process is complete. The applications of hypodermic syringes within a health care facility require the availability of syringes varying particularly in needle length and diameter, and in the dosage capacity of the barrel. To satisfy this need, needles and the remaining portions of syringes are made commercially available both as assembled units, and as separate units allowing the attachment of a selected one of the various needle assemblies to a selected one of various barrels. The Luer lock fittings used to fasten the needle to the barrel form a basis for
It is thus desirable that any improved design for hypodermic syringes should include the capability of switching needles among the syringes. It is even more desirable that any improved design for hypodermic syringes should be capable of using standard needle assemblies, and that the new needle assemblies should be usable in standard syringe barrels.
Modern medical practice dictates that, in order to eliminate a possible source of contagious disease, hypodermic syringes are used only once. There is a growing concern, even when syringes are discarded immediately after use, that health care workers may be accidentally stuck by a hypodermic needle which has been used in the treatment of a patient having a serious communicable disease, such as AIDS or hepatitis. Used hypodermic needles have become an especially dangerous form of waste material, posing a danger to anyone handling trash from a health care facility and to anyone who might come into contact with such material after it has been dumped, and requiring special puncture resistant containers for disposal.
Another problem commonly associated with discarded hypodermic syringes is their potential use by drug abusers, who sometimes search waste material from health facilities for such devices. This practice obviously carries a significant risk of infection to these drug users and to others they may subsequently contact.
Conventional hypodermic syringes included an inward extending ring near the proximal opening of the barrel, which forms a stop, preventing the inadvertent removal of the plunger from the barrel. However, this ring is generally not rigid enough to prevent the deliberate, surreptitious removal of the plunger, as by a drug abuser.
One prior art solution to the aforementioned problems has been to enclose the needle in a sheath manually slipped over the needle end before and after use of the syringe. However, this technique still exposes health workers to the risk of being stuck with an infected needle as the sheath is slipped on, particularly when the needle is not properly aligned with the sheath opening. Furthermore, this technique does nothing to render the syringe useless to a drug abuser.
Another prior art solution to the aforementioned problems is breaking the needle from the syringe once it is used. While this procedure is followed in a number of health care facilities, there are still several disadvantages to this procedure. First, the broken needles are not necessarily enclosed in a way permitting their subsequent safe handling, and second, the additional handling of used needles by health care workers in the process of breaking the needles may increase the risk of their being accidentally stuck by an infected needle.
One attractive solution to the aforementioned problems is in providing a syringe/needle assembly in which the needle may be retracted into the barrel of the syringe after use, so that the needle is held in an envelope formed by the barrel during disposal. The patent literature includes descriptions of devices of a first general type, in which a needle is fastened to a needle carrier which travels axially within the barrel. In its distal position, the carrier holds the needle ready for use at the distal end of the barrel. After the plunger assembly is moved to the distal end of the barrel, after dispensing the desired medication, the plunger assembly engages and locks onto the needle carrier. When the plunger assembly is subsequently withdrawn and returned to the proximal end of its travel, the needle is carried with the plunger until it is completely enclosed within the barrel. At this point, the syringe ready for proper and safe disposal. Examples of syringes of this type are found in U.S. Pat. No. 4,710,170, issued to Haber et al on Dec. 1, 1987; in U.S. Pat. No. 4,790,822, issued to Haining on Dec. 13, 1988; and in U.S. Pat. No. 4,883,471, issued to Braginetz et al on Nov. 28, 1989.
In the prior art devices, the needle is fastened to the needle carrier by conventional means. For example, needle may be fastened to a Luer lock hub, which, in turn, is screwed onto a threaded hole forming internal surfaces in the needle carrier. Thus, syringes of this kind have the advantage of being capable of using standard needle assemblies of the types widely available for syringes not incorporating the safety feature of needle retraction. If the syringe is provided with its needle carrier at the distal position, an interchangeable needle may be screwed into the syringe from the distal end, in the conventional manner. However, the barrels of syringes of this type, of necessity, have relatively large openings at their distal ends, to accommodate the motion of the needle, together with a portion of the needle carrier as it is retracted into the barrel. This large opening, in turn, significantly increases the complexity and cost of the device by requiring fluid tight sealing around the outside of the needle carrier, so that medicine can be dispensed through the needle without leakage out of the distal end of the syringe.
Furthermore, the needle carrier of the prior art devices occupies a significant portion of the axial length of the barrel. The conservation of distance along this length is especially important in a syringe having a retractable needle because the space is needed for storage of the needle after use. Conventional syringes are built to particular sizes for convenient handling and use, as well as for various barrel capacities for medication. For example, the barrels of typical syringes having either three cubic centimeter and five cubic centimeter capacities are about 2.5 inches in length, with the difference in capacity being accomplished by varying the diameter. A typical long needle extends 1.5 inches from the end of the Luer hub to which it is attached. Including this hub, the length of the needle assembly is about 2.125 inches. Thus, the use of a needle carrier of the prior art requires lengthening the barrel beyond the length necessary for handling and capacity, thereby decreasing the ease and familiarity with which the syringe is handled and further increasing its costs of manufacture and distribution.
The device of U.S. Pat. No. 4,883,471 to Braginetz et al mounts the needle carrier in a second piston. After the medication is dispensed, vent ports are opened by rotating a cap at the distal end of the syringe, so that the atmosphere is allowed to enter the syringe at the distal end of this second piston. The retraction of the piston, with the needle, is then accomplished by the differential pressure established as the plunger is withdrawn. However, rotating the cap in this way presents the health care worker with the inconvenience of an extra step in the process.
The patent literature also describes devices of a second general type, in which the needle assembly is loaded into the syringe barrel from inside the barrel, to stick outward through a relatively small opening in the distal end of the barrel. After the injection of medicine by means of the plunger assembly, the needle assembly is attached to the distal end of the plunger assembly to be retracted into the syringe barrel as the plunger assembly is pulled back toward the proximal end of the barrel.
While syringes of this type address the concerns expressed above relative to the use of a separate needle carrier, they lack the important ability to use conventional needle assemblies, which are adapted to be screwed into place using Luer couplings from outside the distal end of the barrel. In addition, if interchangeable needles are to be used in any way on the syringes, they must be attached by relatively difficult or complex means within the barrels. Further, by changing a needle through the barrel, the sterility of the barrel can be violated.
Some devices of this second general type, in which the needle is loaded from inside the barrel, include couplings between the needle assemblies and the distal ends of the barrels, which are connected and disconnected by the rotation of the needle assembly within the barrel, being described, for example, in U.S. Pat. No. 4,507,i17, issued to Vining et al on Mar. 26, 1985; in U.S. Pat. No. 4,675,005, issued to DeLuccia on Jun. 23, 1987; in U.S. Pat. No. 4,747,830, issued to Gloyer et al on May 31, 65 1988; in U.S. Pat. No. 4,919,652, issued to Alter et al on Apr. 24, 1990; and in U.S. Pat. No. 4,986,813, issued to Blake III et al on Jan. 22, 1991. While DeLuccia, Alter, and Blake III teach the use of threaded screw connections, Vining and Gloyer uses quick release, quarter turn types of connection. Vining also describes means for providing the syringe, before use, with the needle retracted for safe handling. A disadvantage of these syringes is the additional requirement that the plunger must be twisted after an injection is given, before disposal of the syringe with the needle assembly in a retracted position. This twisting is needed to engage the needle assembly to the plunger assembly, and to disengage the needle assembly from the distal end of the barrel. However, this requirement places a burden on health care workers in an emergency situation, and can be expected to result in a failure to properly retract needles in some units before disposal.
Other devices of this in which the needle is loaded through the barrel interior include means for engaging the proximal end of the needle assembly with a mechanism extending from the distal end of the plunger assembly as the plunger mechanism reaches the distal end of its travel in dispensing medicine through the needle. Such devices are described, for example, in one of the embodiments of U.S. Pat. No. 4,675,005 to DeLuccia; in one of the embodiments of U.S. Pat. No. 4,692,156 to Haller; and in U.S. Pat. No. 4,804,370, issued to Haber et al on Feb. 14, 1989. In this Haber device, the needle extends outward through a small hole at the distal tip of the syringe barrel. The proximal end of the needle is provided with a flange, and the plunger assembly is provided with a needle capturing receptacle which engages this flange as the plunger assembly is moved to the distal end of the barrel, so that the needle is subsequently retracted into the barrel as the plunger assembly is withdrawn.
While such devices are operable without requiring the additional step of twisting the plunger after medicine is dispensed, they are still inconvenient to use, when compared to conventional syringes, because they do not accept conventional needle assemblies, and because, if it is necessary to install any type of needle assembly, the installation procedure is relatively complex and would violate the integrity of the sterility.
An important consideration in the design of a hypodermic syringe is the ability of the device to transmit axial forces to the needle from the barrel and plunger. Forces as high as several pounds may be required, both to insert the needle into the patient, and to withdraw the needle from the patient during the process of giving an injection. If the needle is to be retracted into the barrel of the syringe, means must be provided to prevent this retraction during the insertion of the needle into the patient, due to the necessary application of force to the needle as it is inserted.
In the devices having needle assemblies connected to the barrels with screw threads or quarter turn fasteners, to be disconnected by rotation of the plunger after the medication is dispensed, these fasteners prevent premature retraction of the needle. These devices are shown, for example, in U.S. Pat. Nos. 4,507,117, 4,675,005, 4,747,830, 4,919,652, and 4,986,813. While this method of holding the needle in place during injection is quite effective, the disadvantages of requiring the performance of the additional manual rotation step and nonstandard components remains.
In those devices having means for engaging the proximal end of the needle assembly with a mechanism extending from the distal end of the plunger assembly, the connection between the needle and the barrel must be strong enough to hold the needle in place as it is inserted into the patient. Further, the needle must subsequently be pulled directly out of this connection for retraction. Both of these actions are accomplished by applying an axial force to the needle. In the devices of U.S. Pat. No. 4,692,156 to Haller, the needle is mounted in an aperture within a deformable tapered mounting post, which deforms to slide through a passage in the barrel during retraction. In other devices, as shown, for example in U.S. Pat. Nos. 4,804,370 and 4,826,484 to Haber et al., the needle is retained by a tight fit within a distal hole of the barrel. This means that, for reliable operation, the force which must be applied for needle retraction, to overcome the attachment between the needle and the barrel, must be greater than the highest force expected during the insertion of the needle into the patient, together with a safety factor applied to cover variations in the process of manufacturing the syringe. If the needle is to be retracted during withdrawal from the patient, this force must be even higher. The requirement to apply such a large force places a significant burden on health care personnel and creates a potential danger to the patient.
The device described in U.S. Pat. No. 4,710,170 to Haber et al includes a needle carrier which is held in place within the barrel by means of a quick release fastener. After the dispensing of medication is completed, the plunger is manually rotated to release the carrier from engagement with the barrel. Thus, a requirement to perform an additional step is placed on health care personnel.
The device described in U.S. Pat. No. 4,790,822 to Haining includes a needle carrier which is held in place at the distal end of the barrel by opposing shoulders extending inward from the interior of the barrel. As the plunger is moved to the distal end of the barrel, a piston at the distal end of the plunger forces these shoulders apart, releasing the carrier to return with the plunger.
The patent literature also describes apparatus for causing the needle to be rotated transversely, about its attachment to the plunger as it is retracted into the barrel, to point toward a side of the barrel. This is done to prevent accidental or deliberate extension of the needle through the hole in the distal end of the barrel, by means of pushing the plunger inward. In other words, this feature provides further safety for health care and trash disposal workers, and goes another step toward preventing the subsequent use of the syringe by drug abusers. For example, U.S. Pat. No. 4,804,370, issued to Haber et al on Feb. 14, 1989, describes needle capturing receptacle with legs, for capturing a flange at the proximal end of the needle. Two of the legs are shorter than the others, so the needle is rotated transversely as it is retracted. As described in U.S. Pat. No. 4,986,813 to Blake III et al, a syringe includes a fitting fastening the needle assembly to the distal end of the plunger for retraction with a slot, extending inward from one side of the fitting, which is allowed to expand as the needle is fully retracted, throwing the needle out of alignment with the longitudinal axis of the plunger.
Blake III also describes the use of stopping surfaces extending into the barrel near its proximal end, angled to prevent removal of the plunger from the barrel, while allowing its assembly into the barrel as the syringe is fabricated. Such surfaces make it particularly difficult for a drug user to take the syringe apart to make it again operable or to retrieve the needle.
Thus, while the feature of needle retraction can be accomplished in a number of ways, the methods proposed in the prior art for providing this feature all have various disadvantages. What is needed is apparatus for providing needle retraction without substantially increasing the size or length of the syringe, as required when a separate needle carrier is employed, and without requiring the performance of an additional step, such as the rotation of the plunger, by health care personnel. Since health care facilities must carry a relatively large inventory of different sizes and types of syringes and needles, it is desirable that an improved syringe should accept the removal and attachment of needles in the standard way, from outside the distal end of the barrel. It is further desirable that the needle be releasibly held in place by positive means, such as a latch or movable abutting surface, rather than by reliance on a tight fit. Also, since conventional hypodermic syringes are low cost items used in large quantities by health care facilities, it is particularly desirable that the feature of needle retraction should be provided by a mechanism which is inherently simple and low in manufacturing cost. In particular, any improved syringe ideally will use existing syringe parts or slight modified parts so that existing mold tooling can be used.